This invention relates generally to high speed packaging machines and more particularly to a feeder conveyer system for supplying product to the wrapper apparatus at a preset rate and with appropriate spacing between each product so that packages of uniform appearance will be produced.
In high speed packaging machines with which the present invention finds use, products are fed into a film forming station wherein a film, such as cellophane, polyethylene or paper, is formed into a continuous and moving tube about the products as the tube moves in synchrony through sealing and severing stations. In that the film generally has labels and other graphic material thereon, it is essential that the products, at all times, be synchronized with the film if the wrapped products are to look identical upon exit from the packaging machine. For exemplary purposes and with no limitation intended, let it be assumed that the products being wrapped are candy bars. The unwrapped bars exiting from the chocolate coating station normally travel along a cooling conveyer and, when sufficiently cool, are swept in batches from a holding platform onto a first conveyer belt which is arranged to pass just beneath converging vertical side walls of a guide so that the bars will be oriented in a serial train, one behind the other. At this point, however, the spacing between each bar is random, there being gaps of differing lengths between adjacent bars. Next, the bars are transferred to a backlog belt controlled by an electric eye. If a space between two adjacent bars is noted, the conveyer preceding the backlog belt is speeded up, allowing the later arriving bars to catch up to the preceding one. Where no space between bars is detected, the belt or belts leading to the backlog belt is again made to move at its slower rate. Thus, upon exiting the backlog belt, the bars are in a serial train with no gaps between adjacent bars.
Next, it is desired that the bars be spaced from one another by a predetermined amount so that they may be fed, via a transfer conveyer, into the in-feed conveyer of the wrapper system. The spacing is achieved by a further conveyer belt, termed the separation belt, which is driven by an electronically controlled servo motor. It is desired that the separation belt be driven sufficiently fast to space the bars correctly to fit within a flight, i.e., between adjacent pusher fingers on the side chains comprising the transfer conveyer. The side chains are driven in synchronism with the in-feed conveyer of the wrapper, such that if the bars are properly oriented with respect to the transfer conveyer, they will also be properly deposited between pushers comprising the wrapper's in-feed conveyer. Thus, the key is to appropriately control the speed of the separation belt such that the specified spacing between adjacent products results.
In prior art systems of the type thus far described, it is not uncommon for an empty space to occur on the backlog belt. Also, occasionally, the products, e.g. candy bars, do not separate cleanly as they pass from the backlog belt to the separation belt. This often leads to product damage as the products become pinched between opposed pusher fingers attached to the side chains of the transfer conveyer or alternatively, empty wrappers may exit the machine. It will also be apparent to those skilled in the art that the first products into a previously empty feeder arrive at the separation belt asynchronously with respect to the transfer mechanism. Thus, in the prior art systems, operator intervention is required upon start-up to insure proper operation of the packaging machine.
The present invention constitutes an improved control system for a feeder conveyer associated with a high speed packaging machine. Specifically, the control system of the present invention is capable of sensing the position of a product on a separation belt relative to the position of a flight on the side chains of the transfer conveyer with that flight being arbitrarily divided into a plurality of discrete zones. Associated with each of these zones is a predetermined change in speed of the separation belt. Thus, for example, a photocell arrangement disposed one flight length from the end of the separation belt is used to sense the leading edge of each product passing across that belt. An absolute shaft encoder and associated electronics provide signals indicative of, for example, five zones making up a side chain pusher flight. If it is assumed that the product, at the time its leading edge is sensed, is slightly too far forward for correct placement between two pusher fingers on the side chains, the separation belt will be made to slow down and the amount of the slowdown will be dependent upon just how far the product is out of time in relation to the zones defined by the shaft encoder. If the product is slightly too far backward relative to the pusher fingers of the infeed conveyer at the time its leading edge is sensed, the separation belt will be made to speed up. Again, the rate of speed increase depends upon the position of the product in relation to the zones defined by the absolute shaft encoder at the time that the leading edge of the product passes a fixed electric eye.
The control system further includes a storage register which is clocked upon receipt of a leading edge signal from the electric eye and which captures the output from the shaft encoder. The outputs from this register are individually connected to a velocity servo control loop, the result being that the speed change signal to the motor driving the separation belt is a function of the degree to which the product leads or lags its ideal orientation for proper meshing with the flights of the transfer conveyer.